My presentation at WDSA 2014, Bari, Italy: Water distribution systems are prone to be contaminated. Following a contamination event the contaminated section of the water distribution system should be identified, isolated and cleaned before it is returned to service. The cleaning process includes flushing and disinfection. While there are number of disinfection methods (for example: tablet, continuous and slug) they all require that the disinfectants will have minimal contact time (T) in a predefined concentration (C) with the pipe. The regulatory agencies such as the ministry of health in Israel publishes procedures for the disinfection of water mains in which usually a short part of a single main is considered and no specific procedures are given for larger portions of the water system. This study presents an optimal operation plan for disinfection of water distribution systems taking into account the locations where the disinfectants should be injected into the network, their concentration, injection times, flow rate and drainage locations. The method is a GA-EPANET framework. It is demonstrated on a small real-world network section.

1. OPTIMAL DISINFECTION OF WATER
DISTRIBUTION NETWORKS FOLLOWING A
CONTAMINATION EVENT
Avi Ostfeld, Technion
Elad Salomons, OptiWater
WDSA 2014, Bary, Italy, 14-17 July

2. Acknowledgment
This study was supported by the joint Israeli Office of
the Chief Scientist (OCS) Ministry of Industry, Trade
and Labor (MOITAL) and by the German Federal
Ministry of Education and Research (BMBF), under
project number GR_2443
WDSA 2014, Bary, Italy, 14-17 July

3. Network wide contaminations events
• Water outage of several days
• Caused by chemicals, sewage, backflow, human
errors …
• Fortunately they are rare
• Unfortunately they have a wide effect making life
very difficult
• Well, not as difficult as having a slow Internet
connection…
WDSA 2014, Bary, Italy, 14-17 July

4. Must have a cat…
WDSA 2014, Bary, Italy, 14-17 July

5. Kiryat Motzkin, Israel, 2011
• E. Coli detected in water samples
• Effected 47,000 residents
• 8 days without potable water
• Treatment: flushing
WDSA 2014, Bary, Italy, 14-17 July

6. Elk River, US-WV, 2014
• Chemical spill (4-Methylcyclohexanemethanol)
• Effected >300,000 residents
• 6 days without potable water
• Tens hospitalized
• Treatment: flushing and Carbon
WDSA 2014, Bary, Italy, 14-17 July

7. So …
If there is a system wide contamination,
what about a system wide disinfection?
(following a contamination, not regular operation)
WDSA 2014, Bary, Italy, 14-17 July

8. Regulation and standards
• In Israel the regulation are by the Ministry of Health
– “Potable water distribution systems cleaning
regulations” (sorry, only in Hebrew)
• The regulations are for water tanksreservoirs and a
single water main.
• No regulations for networks.
• In general, the regulations define “Ct”, where
• C is the disinfectant minimum concentration, and
• t is the minimum contact time with the waterpipe
WDSA 2014, Bary, Italy, 14-17 July

9. WDSA 2014, Bary, Italy, 14-17 July
read this way
methodCtapplication
mg/Lhr
Fully fill the pipe with Chlorine solution,
seal it, wait and flush

10. AWWA Standard C651-05
• “Disinfecting Water Mains”
• Different disinfection methods:
• Tablet – 25mg/L for 24 hours
• Continuous feed – 25mg/L for 24 hours
• Plug – 100mg/L for 3 hours
• Appendix C – Disposal of Heavily Chlorinated Water
• Check with local sewer department…
• Chlorine residual of water … will be neutralized….
WDSA 2014, Bary, Italy, 14-17 July

11. Simple explanation
WDSA 2014, Bary, Italy, 14-17 July
source
Injection point
50mg/L
“dead-end”
drain
drain

12. Problem formulation
• Objective:
• disinfect the network in minimum time, or
• disinfect the network with minimum disinfectant
• Decision variables:
• disinfectant injection locations and flows
• drainage locations and flows
• Constraints:
• number of drainage locations
• minimum concentration throughout the network (C)
WDSA 2014, Bary, Italy, 14-17 July

13. WDSA 2014, Bary, Italy, 14-17 July
Power generator Hypochlorite tank Dosing pumps
Image courtesy of MODOtec LTD.

14. WDSA 2014, Bary, Italy, 14-17 July
Image courtesy of MODOtec LTD.

15. The real network
WDSA 2014, Bary, Italy, 14-17 July
Image removed.

16. WDSA 2014, Bary, Italy, 14-17 July

17. The modified network
WDSA 2014, Bary, Italy, 14-17 July

18. Simplified problem
WDSA 2014, Bary, Italy, 14-17 July

19. Methodology
• Genetic Algorithm linked with EPANET
• Simple binary representation
• Select 2 drainage locations (out of 6 options)
• Select 5 drainage flows (2 for new locations + 3
fixed)
• Minimum concentration at all junctions – 50mg/L
WDSA 2014, Bary, Italy, 14-17 July

20. The program
WDSA 2014, Bary, Italy, 14-17 July

21. Sensitivity analysis
WDSA 2014, Bary, Italy, 14-17 July
2
3
4
5
6
7
1 2 3 4 5 6
Operationtime(hr)
Number of drainage locations

22. Further research
• Different disinfection methods
• Time based drainage
• Multiobjective formulation
• And more…
WDSA 2014, Bary, Italy, 14-17 July

23. Thank you
Questions?
selad@optiwater.com
WDSA 2014, Bary, Italy, 14-17 July